Many problems exist with the installation of electrical transmission, distribution, or underground lines. Electrical transmission, distribution, and underground lines are commonly referred to as “conductors.” Conductors transport electrical energy from a generation source to at least one distribution point, and from distribution points to end users. These types of conductors are heavy, have large diameters, and are difficult to handle. Conductors are typically composed of aluminum bands wound around a steel core.
Conductors can be damaged if they come in contact with the ground or other objects. Therefore, tension conductor stringing, as opposed to slack conductor stringing, is generally the only acceptable method of installing conductors. During tension stringing, conductors can be damaged if tension beyond the specified maximum is applied during installation. It is desirable to install conductors in a more efficient, controlled, and safe manner. In addition, it is critical that conductor tension specifications are not exceeded.
In addition to conductors, fiber optic systems are also installed on transmission lines and distribution systems. Types of fiber optic systems include optical ground wire (OPGW), all dielectric, self supporting (ADSS) cables and optical fiber installed in high-density polyethylene (HDPE) conduits. These types of cables are generally more susceptible to damage from excess tension.
Conductor installation using the tension stringing process involves the removal of conductor from a supply reel at a speed and tension within specified parameters. Prior to stringing operations, towers or poles (hereinafter referred to as “structures”) are installed. The structures have several arms to which insulator strings are attached. Stringing blocks, which are large wheels or “sheaves” attached to a housing, are connected to the insulator strings. Hard line cable is unwound from the hard line drum puller and placed in the stringing blocks for a section of structures. When installing a smaller diameter conductor, pulling rope may be used in place of hard line cable.
At the opposite end of the rope or hard line cable drum puller, reels of conductor are mounted on reel stands. After the hard line is installed, it is attached to the conductor. The hard line is then recoiled, pulling the conductor back through the stringing blocks. This is often referred as the “pulling” operation. When stringing or pulling is complete, the line is said to be “pulled in.” Once pulled in, the stringing blocks are removed and the conductor is attached or “clipped in” to the structures.
During the pulling operation, power to the drum must be continuously adjusted to maintain the speed of the conductor and to maintain constant tension on the conductor as it moves through the stringing blocks. Continuous adjustments to power are necessary because of the continuous change in the diameter of the pulling drum as the pulling line is retrieved thereby causing conductor to be removed from the conductor supply reel. Excessive tension during installation can damage the conductor. A damaged conductor can cause voltage drops, corona losses, reliability issues, and catastrophic failure. Therefore, it is essential to maintain a constant pulling tension within the design parameters. In addition, a conductor can jam in a stringing block. Without a mechanism to automatically sense the increase in tension and make adjustments, including shutting down the pull if necessary, structures and equipment can be severely damaged.
The delays to a project caused by a conductor jam in a stringing block can be excessive. A damaged conductor may have to be removed and replaced. If a structure is damaged, the structure may have to be replaced. This may entail time to order and manufacture a new section as well as the time needed to perform the replacement.